Foto :

EN : Zebra

FR : Zèbre

ES : Cebra

Zebras are African equids best known
for their distinctive white and black stripes. Their stripes come in
different patterns unique to each individual. They are generally social
animals and can be seen in small harems to large herds. Zebras are generally
2.3 m (8ft) long, stand 1.25-1.5 m (4-5ft) at the shoulder, and weigh
around 300kg (660 lbs), although some can grow to more than 410 kg (900
lbs). In addition to their stripes, zebras have erect, mohawk-like manes.
Unlike their closest relatives, horses and donkeys, zebras have not
been truly domesticated. There are three species of zebra: the Plains
Zebra, Grevy's Zebra and the Mountain Zebra. The Plains zebra and the
Mountain Zebra belong to the subgenus Hippotigris, but the Grevy's zebra
is the sole species of subgenus Dolichohippus. The latter resembles
an ass while the former two are more horse-like. Nevertheless, DNA and
molecular data show that zebras do indeed have monophyletic origins.
All three belong to the genus Equus along with other equids. In certain
regions of Kenya, Plains zebras and Grevy's zebras coexist. Zebras might
have lived in North America in prehistoric times.

The unique stripes and behaviors of zebras
make these among the most familiar animals to people. They can be found
in a variety of habitats, such as grasslands, savannas, woodlands, thorny
scrublands, mountains and coastal hills. However, various anthropogenic
factors have severely impacted zebra populations, in particular hunting
for skins and habitat destruction. The Grevy's zebra and the Mountain
zebra are endangered. While the Plains zebras are much more plentiful,
one subspecies, the quagga, went extinct in the late nineteenth century.
There are three extant species, as well as several subspecies. Zebra
populations vary a great deal, and the relationships between and the
taxonomic status of several of the subspecies are well known. Zebra
species may have overlapping ranges, they do not interbreed.

This held true even when the Quagga and
Burchell's race of Plains Zebra shared the same area. According to Dorcas
McClintock in "A Natural History Of Zebras," Grevy's zebra
has 46 chromosomes; plains zebras have 44 chromosomes and mountain zebras
have 32 chromosomes. In captivity, Plains Zebras have been crossed with
mountain zebras. The hybrid foals lacked a dewlap and resembled the
Plains Zebra apart from their larger ears and their hindquarters pattern.
Attempts to breed a Grevy's zebra stallion to Mountain Zebra mares resulted
in a high rate of miscarriage.

Zebras were the second species to diverge
from the earliest proto-horses, after the asses, around 4 million years
ago. The Grevy's zebra is believed to have been the first zebra species
to emerge. Zebras are black with white stripes and their bellies have
a large white blotch for camouflage purposes. These stripes are typically
vertical on the head, neck, forequarters, and main body, with horizontal
stripes at the rear and on the legs of the animal.

Zebras are black or dark animals with
white stripes and their bellies have a large white blotch for camouflage
purposes. Some zebras have brown "shadow stripes" in between
the white and black coloring. Zebras are described as black with white
stripes rather than the reverse for the following three reasons:
White equids would not survive well
in the African plains or forests.
The quagga, an extinct Plains zebra
subspecies, had the zebra striping pattern in the front of the animal,
but had a dark rump.
When the region between the pigmented
bands becomes too wide, secondary stripes emerge, as if suppression
was weakening.

The fact that some zebras have pure white
bellies and legs is not very strong evidence for a white background,
since many animals of different colors have white or light colored bellies
and legs.The stripes are typically vertical on the head, neck, forequarters,
and main body, with horizontal stripes at the rear and on the legs of
the animal. The "zebra crossing" is named after the zebra's
black and white stripes. Some zoologists believe that the stripes act
as a camouflage mechanism. This is accomplished in several ways. First,
the vertical striping helps the zebra hide in grass. While seeming absurd
at first glance considering that grass is neither white nor black, it
is supposed to be effective against the zebra's main predator, the lion,
which is color blind. Theoretically a zebra standing still in tall grass
may not be noticed at all by a lion. Additionally, since zebras are
herd animals, the stripes may help to confuse predators - a number of
zebras standing or moving close together may appear as one large animal,
making it more difficult for the lion to pick out any single zebra to
attack. A herd of zebras scattering to avoid a predator will also represent
to that predator a confused mass of vertical stripes travelling in multiple
directions making it difficult for the predator to track an individual
visually as it separates from its herdmates, although biologists have
never observed lions appearing confused by zebra stripes.

Stripes are also believed to play a role
in sexual attractions, with slight variations of the pattern allowing
the animals to distinguish between individuals.A more recent theory,
supported by experiment, posits that the disruptive colouration is also
an effective means of confusing the visual system of the blood-sucking
tsetse fly. Alternative theories include that the stripes coincide with
fat patterning beneath the skin, serving as a thermoregulatory mechanism
for the zebra, and that wounds sustained disrupt the striping pattern
to clearly indicate the fitness of the animal to potential mates.